Men with recent myocardial infarction or angina, known to be at high risk for sudden coronary death, are identified from a population of about 150,000 men aged 35 to 74 enrolled in the Health Insurance Plan of Greater New York (HIP). They are invited to special examination sessions at which information pertinent to development of prognostic data is collected according to a standard protocol. At these examinations, and at several subsequent sessions, the men are monitored with a single ECG lead recorded on a tape cassette. The ECG tapes are processed by computer and all abnormal beats written out on ECG paper. Trained readers and physicians review these writeouts to identify all ventricular premature beats (VPB) and characterize other features of ventricular ectopic activity. The monitored men (estimated at 2,000 by the end of the study) are followed for mortality, and information from next of kin on circumstances of death is obtained to supplement all medical record abstracts. Analysis will include multivariate approaches directed at estimating the contribution of ventricular ectopic activity to risk of sudden coronary death.